Biomarker assessment of organic matter sources and degradation in Canadian High Arctic littoral sediments

Carbon stocks in the High Arctic are particularly sensitive to global climate change and the investigation of the variation in organic matter (OM) composition is beneficial for improved understanding of OM vulnerability. OM biomarker characterization of solvent–extractable compounds and CuO oxidation products of littoral sedimentary OM in the Canadian Arctic was conducted to determine OM sources and decomposition patterns. The solvent–extracts contained a series of aliphatic lipids, steroids and one triterpenoid of higher plant origin as well as the low abundance of iso- and anteiso-alkanes originating from Cerastium arcticum (Arctic mouse-ear chickweed), a native angiosperm. The carbon preference index (CPI) of the n-alkane, n-alkanol and n-alkanoic acid biomarkers suggests relatively fresh lipid material in the early stages of degradation. The CuO oxidation products were comprised of benzenes, lignin-derived phenols and short–chain diacids and hydroxyacids. A high abundance of these terrestrial biomarkers at sites close to the river inlet suggests soil-derived fluvial inputs are an important source of OM delivered to the littoral sediments. The high lignin-derived phenol ratios of acids to aldehydes suggest that lignin degradation is in a relatively advanced oxidation stage. The absence of ergosterol, a common fungal biomarker also suggests that lignin-derived OM may be preserved in soil OM and transported to littoral sediments. This representative OM characterization suggests that Arctic sedimentary OM is a mixture of recently deposited and/or preserved lipids in permafrost melt and oxidized lignin-derived OM that may become destabilized from external influences such as climate change.